This invention relates to a variable valve timing control apparatus provided in an internal combustion engine (hereinafter referred to as xe2x80x9can enginexe2x80x9d) to change the valve timing of intake valves or exhaust valves, thereby changing operation timing of the intake valves or the exhaust valves in accordance with engine conditions. A variable valve timing control apparatus is proposed in an engine to displace the rotational phrase of a camshaft and adjust the valve timing of either an intake valve or an exhaust valve.
This type of apparatus is generally known. For example, relevant related art is disclosed in Japan publication (koukai) No. 9-280018, and Japan publication (koukai) No. 10-159515. These publications disclose a vane-type variable valve timing control apparatus (hereinafter referred to as xe2x80x9cvane-type VTCxe2x80x9d or simply xe2x80x9cVTCxe2x80x9d) which has a housing member rotated by a crankshaft of the engine. The housing has a circular space and fan-shaped spaces protruding from circumferential surface of the circular space. A vane rotor is accommodated in the housing member and rotates in synchronism with a camshaft. There are plural vanes protruding from the circumferential surface of the vane rotor, each vane is accommodated in each fan-shaped space and defines an advancing hydraulic chamber and a retarding hydraulic chamber. Finally, there is a hydraulic actuating means for actuating hydraulic pressure in the advanced hydraulic chambers and the retarding hydraulic chambers. The hydraulic actuating means selectively supplies the hydraulic fluid to either the advancing hydraulic chambers or retarding hydraulic chambers and discharges the hydraulic fluid from the other of the advancing hydraulic chambers and retarding hydraulic chambers. Thereby the vane rotor is rotated relative to the housing.
The Japan publication No. 9-280018 further describes a locking mechanism for preventing a vane rotor from relatively rotating with respect to a housing. The locking member comprising a locking pin provided in a vane, and an engaging bore provided in the housing. When the engine is out of operation, or when the hydraulic pressure in the advancing hydraulic chambers or the retarding hydraulic chambers is under a predetermined value, a leading head portion of the locking pin is urged into an engaging bore by the urging force of a spring provided in the locking pin. As a result, an impinging sound that otherwise would be caused by the relative movement of the vanes and the housing member is prevented from being generated even if the camshaft undergoes positive or negative torque variation in driving the intake valves or exhaust valves, when the vanes are disposed at the most retarded position or the most advanced position in respect of the crankshaft. When the pressure in the advancing chambers or the retarding chambers is over the predetermined value by supplying hydraulic fluid to the advancing hydraulic chambers or the retarding hydraulic chambers, the leading head portion of the locking pin is retracted from the engaging bore and the vane rotor relatively rotates with respect to the housing member. The leading head portion and the engaging bore are both formed cylindrically.
However, since the both leading head portion and the engaging bore are formed cylindrically, a diameter of the engaging bore must be made larger than a diameter of the leading head portion of the locking pin in order that the leading head portion is accommodated positively in the engaging bore. As a result, a gap is made between the leading head portion and the engaging bore. This gap causes impinging between the leading head and the engaging bore by torque fluctuation of the camshaft undergoing the positive or negative torque variation.
The Japan publication No. 10-159515 also describes a locking pin of which the leading head portion is provided with a tapered surface, and an engaging bore provided with a tapered surface. Both taper angles correspond together.
However, since these tapers of the leading head portion and the engaging bore should be provided with precisely the same angle, it often is difficult to provide a taper angle of the leading head portion that corresponds to the taper angle of the engaging bore. If the taper angle of the engaging bore is larger than the taper angle of the leading head portion, a gap is provided between the entire outer surface of the leading head portion and the entire inner surface of the engaging bore. Thereby, the locking pin easily fits into the bore, thus allowing the leading head portion to be retracted from the engaging bore by torque fluctuation of the camshaft before the pressure in the advanced hydraulic chamber or the retarded hydraulic chambers reaches a predetermined value.
Even if the leading head portion of the locking pin and the engaging bore can be shaped so that the both taper angles correspond together, the torque fluctuation transmitted via the camshaft and the locking pin affects the whole surface of the engaging bore. This contact causes abrasion at the inner surface of the engaging bore. Thereby a gap is formed between the inner surface of the engaging bore and the outer surface of the leading head portion of the locking pin. Consequently, the locking pin may retract from the engaging bore by torque fluctuation of the camshaft before reaching the pressure in the advanced hydraulic chamber or the retarded hydraulic chambers to the predetermined value.
Accordingly, in view of above-described problems encountered in the related art, a principal object of the present invention is to provide a vane-type VTC which has a locking mechanism that is moved easily and consistently.
Another object of the present invention is to prevent the undesirable retraction of a locking member from an engaging bore.
Still another object of the present invention is to prevent the performance of the apparatus from degradation due to abrasion of the locking mechanism over time.
Yet another object of the present invention is to provide a locking mechanism having a locking member that is highly responsive.
In order to achieve these and other objects, there is provided a variable valve timing control apparatus for an internal combustion engine, having a first shaft and a second shaft, that comprises a housing member rotated in synchronism with one of the first shaft and the second shaft. The housing has a circular space provided inside of the housing and at least one fan-shaped space radially extending from an outer circumferential surface of the circular space, a vane rotor rotated in synchronism with the other of the first shaft and the second shaft and accommodated in the housing member in order to relatively rotate with respect to the housing member. The vane rotor has radially extending at least one vane so as to divide each the at least one fan-shaped space into a first chamber and a second chamber. There is a locking member provided in one of the housing member and the vane, the locking member having a leading head portion provided with tapered surface having a diameter that decreases toward an end face of the leading head portion. The locking member is movable in response to hydraulic pressure in the first hydraulic chamber or the second hydraulic chamber. There also is an engaging bore provided in the other of the housing member and the vane for accommodating the leading head portion, the engaging bore having an opening where the engaging bore accommodates the leading head portion. The diameter at the opening of the engaging bore is larger than a diameter at the end face of the leading head portion, and smaller than a diameter at a position where the leading head portion has the largest diameter.